Viscoelastic Parameters of a Side-Chain Nematic Polymer: II—Analysis of NMR Results in Terms of the Anisotropic Dumbbell Model

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Abstract
The two viscoelastic parameters of a siloxane side-chain nematic polymer—twist viscosity coefficient, and static order parameter—deduced from the NMR study of Reference 1, are discussed in terms of the anisotropic dumbbell model of Brochard using structural information obtained by small angle neutron scattering. It is found that this model, originally developed for dilute solutions of flexible polymers in low molecular mass nematics, describes satisfactorily the data, supporting the idea that the backbone polymer chains are not entangled in the nematic melt. An average elastic constant is deduced. This constant is found to increase sharply as the nematic-smectic A phase is approached. The twist elastic constant is calculated using splay and bend elastic constant values of a very similar polymer. Some (possibly only apparent) difficulties associated with the dumbbell model are pointed out.